This invention relates to electrical interconnect devices.
Anisotropic Conductive Elastomer (ACE) is a composite of conductive metal elements in an elastomeric matrix that is normally constructed such that it conducts along one axis only. In general, ACE is made to conduct through its thickness. One form of ACE material is made by mixing magnetic particles with a liquid resin, forming the mix into a continuous sheet, and curing the sheet in the presence of a magnetic field. This results in the particles forming a large number of closely spaced columns through the sheet thickness. The columns are electrically conductive. The resulting structure has the unique property of being both flexible and anisotropically conductive. These properties provide for an enabling interconnection medium which, when combined with other technologies, make it possible to realize new interconnect capabilities.
ACE materials require that they be compressed between top and bottom conductors to provide the interconnection. This is normally done by compressing the system using a backing plate and spring arrangement. One example of such is shown in FIG. 1. This system can be used only with boards 12 which are designed to accommodate the backing plate 22, and has holes for the connection hardware 28, 29, to pass through, to connect spring plate 24 (with spring force adjustment screw 26) to pressure member 15. Device 14 is electrically interconnected to board 12 using ACE 20. Heat sink 30 is optional in the system. This can result in a conflict with components mounted under the device and on the back of the board.
ACE material can be married with flexible circuits to provide more dynamic range to an ACE interconnect. The flexible circuit consists of an electrically-insulating material such as polyimide, with opposing conductive pads on the surfaces. The pads are vertically interconnected by plated-through holes. Mounting such a flex circuit to ACE material can provide more vertical compliance to the ACE material. This allows the ACE material to be used in assemblies that are not planar, such as circuit boards with solder mask, in which the circuit board pads are lower than the top of the solder mask, thus creating a small well around each pad and into which the ACE material-based interconnect must protrude in order to make electrical contact with the pads.
BGA (ball grid array) devices are electronic components with solder balls placed in a grid and used for final installation (through a solder reflow process) on a printed circuit board. There are other types of electronic packages in which the invention is relevant, including Land Grid Arrays (LGA). Column Grid Arrays (CGA) have solder columns in place of the ball or pad. Factors such as cost, environment and population density determine which geometry is used.
The present invention combines ACE with an adapter board that eliminates the need for a specially modified main board in order to mechanically compress the ACE.
This invention features an electrical connector for separably, electrically interconnecting an electrical device to a main circuit board using anisotropic conductive elastomer (ACE) as part of the interconnect, the electrical connector comprising an adapter board coupled to the main board on one side, the other side of the adapter board defining connecting lands; a layer of ACE on the other side of the adapter board, the other side of the ACE in contact with the device; and a mechanical compression structure coupled to the adapter board, and that provides a compressive load on the device, the ACE and the adapter board, to accomplish a separable electrical connection between the device and the main board, through the ACE and the adapter board.
The connector may further comprise a heat sink coupled to the compression structure and in communication with the device, for removing heat from the device. The connector may further comprise a thermal conducting medium between the device and the heat sink. The ACE material may be formed by magnetically aligned particles that form columns extending between the top and bottom surface of the ACE.
The connector may further comprise a flex circuit between the device and the ACE. The flex circuit may comprise ball seats on one surface and lands on the other surface. The connector may further comprise an insulating adhesive backfill between the adapter board and the main board, to enhance the stiffness of the adaptor board. The backfill may be epoxy. The connector mechanical compression structure may comprise a plate. The mechanical compression structure may further comprise hinge members and a latch for moving and latching the plate. The mechanical compression structure may comprise a compressive spring element. The mechanical compression structure may further comprise a mechanical member for applying a variable compressive load. The connector may further comprise a spacer frame between at least a portion of the adapter board and the main board, to further thicken and stiffen the adapter.
Also featured is an electrical connector for separably, electrically interconnecting an electrical device to a main circuit board using anisotropic conductive elastomer (ACE) as part of the interconnect, the electrical connector comprising: an adapter board coupled to the main board on one side, the other side of the adapter board defining connecting lands; a layer of ACE on the other side of the adapter board, the other side of the ACE in contact with the device; and a mechanical compression structure coupled to the adapter board, and that provides a compressive load on the device, the ACE and the adapter board, to accomplish a separable electrical connection between the device and the main board, through the ACE and the adapter board; wherein the mechanical compression structure comprises a compressive spring element and a mechanical member for applying a variable compressive load.
The ACE material may comprise conductive particles embedded in an elastomer, the conductive particles defining the conductive columns. The flexible circuit element conductive pathways may comprise conductor-lined openings extending between the opposing faces of the flexible circuit element. The flexible circuit element may further define conductive pads on both faces of the flexible circuit element and in electrical contact with a conductive pathway, to provide electrical contact areas on the flexible circuit element, one contact area for interfacing with the ACE material, and the other contact area for interfacing with an electrical device.
The conductive pads on one face of the flexible circuit element may be annular, each surrounding a conductive pathway. The electrical device may comprise an electrical package with a series of electrical contact members protruding from a face thereof. The protruding electrical contact members may define an external peripheral shape, and the inside of the annular conductive pads may define the same shape, so that a protruding electrical contact member contacts a conductive pad about the entire periphery of the protruding electrical contact member.
The electrical package may comprise a ball grid array (BGA) with a series of external, partially-spherical contact members, and the inside of the annular conductive pads may define a circle having a diameter smaller than that of the spherical contact member, so that the contact member seats in the pad. The contact member may contact the pad such that the angle defined by coplanar radii from the contact member center to the contact member pad contact locations is approximately 90xc2x0.
The electrical package may comprise a land grid array (LGA) with a series of external rectangular contact members, and the conductive pads may be rectangular, to provide effective electrical contact therebetween. The electrical package may comprise a column array (CGA) with a series of external projecting column contact members. The conductive pads on the face of the flexible circuit element in contact with the ACE may be continuous, in order to maximize contact with the conductive columns in the ACE.